Chapter 2 - Structure and Function of Crop Plants

Structure and Function

• Parts of Crop Plants:

  • Crop plants consist of two main parts:

    • Root Part: Underground components

    • Aerial Part: Above-ground components that include stems, leaves, branches, flowers, and fruits.

• Roots and Shoots:

  • Roots serve multiple functions:

    • Anchor the plant

    • Absorb water (H2O) and essential minerals

    • Store starch as an energy reserve.

The Shoot System

• The shoot system constitutes the above-ground portion of the plant.

• Stem Functionality:

  • Transports water and minerals from the roots to leaves.

  • Carries sugars produced in the leaves down to the roots.

• Leaves:

  • Important green structures for photosynthesis.

  • Absorb sunlight energy and carbon dioxide (CO2) to produce food.

  • The food produced is translocated via phloem to other plant parts.

External Structure of Stems

• Stem Functions:

  • Support and conduct water and nutrients.

  • Store photosynthate (products of photosynthesis).

• Key Components of Stems:

  • Nodes: Points where leaves attach.

  • Internodes: Segments between the nodes.

  • Buds: Contain apical meristem and developing leaves, responsible for growth.

Bud Types in Stems

• Types of Buds:

  • Leaf Buds (vegetative)

  • Flower Buds (reproductive).

• Terminal Bud: Located at the tip of the stem, inhibiting lateral bud development via auxin, promoting upward growth.

Impact of Removing the Terminal Bud

• If the terminal bud is removed (pruning), lateral buds will develop, resulting in bushier growth.

• Bud Scales: Modified leaves that protect and cover buds.

• A Naked Bud: Bud without protective scales.

Plant Taxonomy

• Dicotyledonous Plants:

  • Flowering plants containing a pair of leaves or cotyledons in the seed embryo.

• Example Plants:

  • Dicot Plant: Brassica Campestris (mustard).

  • Monocot Plant: Zea Mays (maize).

Germination Types

• Hypogeal Germination: Cotyledons remain below ground (typical in monocots).

• Epigeal Germination: Cotyledons push above ground (typical in dicots).

Leaves: External Features

• A typical leaf comprises:

  • Base: Thickened area where leaf attaches.

  • Petiole: Stalk supporting the leaf.

  • Lamina (Blade): Flat part of the leaf that includes veins, with a prominent midrib.

• Leaf Types:

  • Monocot Leaves: Parallel venation.

  • Dicot Leaves: Netted or branched venation (reticulate).

Leaf Details

• Leaf Arrangement: May be alternate, opposite, or whorled.

• Leaf Margin Types: Range from smooth to toothed or lobed.

• Leaf Shape: Simple (single lamina) vs. Compound (multiple leaflets).

Fruit Structure and Purpose

• Fruit Components: Comprises ovaries where seeds develop.

• Pericarp Types: Can be fleshy (like apples) or dry (like acorns).

• Fruits can have seeds enclosed (like apples) or situated on the periphery (like strawberries).

Pollination and Fertilization

• Pollination Types:

  • Cross-pollination: Transfer of pollen to another plant.

  • Self-pollination: Pollen transfer within the same flower or plant.

• Fertilization occurs when a pollen grain germinates on the stigma, forming a pollen tube that leads to the ovule where fertilization of the egg takes place.

Seed Development

• Zygote: Results from fertilization, developing into an embryo.

• Dormancy: The embryo remains dormant until conditions are favorable for growth.

• Types of seeds include:

  • Endospermic Seeds: Storage reserves outside the embryo (e.g., maize).

  • Non-endospermic Seeds: Food stored within cotyledons (e.g., broad beans).

Types of Roots

• Fibrous Roots: Profusely branched, typical in plants like beans.

• Taproot: Main downward-growing root structure seen in carrots.

• Adventitious Roots: Originating from unexpected places, aiding support.

• Aerial Roots: Help plants like ivy and philodendrons to climb.

Stem Internal Structure

• Apical Meristem: Site of active cell division at stem tips leading to growth.

• Vascular System: Comprises xylem (water transportation) and phloem (sugar transport).

Leaf Internal Structure

• Comprises multiple layers with functions in photosynthesis and gas exchange.

• Stomata: Small openings controlled by guard cells, regulating gas exchange.

Summary of Functions

• Photosynthesis: Leaves produce sugars; roots provide water and minerals; stems transport nutrients.

• Reproduction: Flowers play vital roles in seed production and plant lifecycle.